Fig. 1: In situ SEM tensile testing of single-crystalline graphene monolayers.
From: Experimentally measuring weak fracture toughness anisotropy in graphene
a Experimental setup. Samples were placed on a push-to-pull (PTP) micromechanical device, which is actuated by an external quantitative pico-indenter15. b, c SEM images of Sample 1 at the initial (b) and fractured (c) states in the final loading-unloading cycle. d Stress-strain relations of Sample 1 (black) and Sample 2 (red), showing the brittle fracture features. The apparent nonlinearity arises mostly from the presence of cracks due to the limited size of samples. e, f SEM images of Sample 2 at the initial (e) and fractured (f) states in the final loading-unloading cycle. The dimensions and coordinates are measured on the initial state. The cleaved (upper and lower) edges along the crack paths (from left to right) were marked in (c), (f). The crystalline direction is characterized by TEM and shown in the insets of panels (c), (f). Panels (c), (f) show the non-planar or curling nature of the cleaved edges.
